This isn't a widely-used feature, so I don't have a good handle on its bugs.
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Can you clarify: does dragging over a link (in Quickblock) cause this, even if you start on, say, an image?.. or just if you start on a link?

Unfortunately, there's a limitation in the w3c-spec for event-listeners: once they've been added, they can't be listed out without knowing exactly the code as which they were assigned. Thus, they can't be anonymously removed.
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Calling the standard event-cancellations does nothing to deter listeners registered at the same level as Adblock.
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This looks like an indefinitely open bug.

Org:
Ctrl+shift+k is the shortcut to disable Quickblock. I'm not sure how I'll resolve this, since Quickblock needs to cancel the first click in anticipation of a second-click coming -- many ad-areas have listeners on the first click.
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Maybe, instead, I could set it to activate on hover: ctrl+shift+mousemove.

Personnally I think that the old Quickblock behaviour was fine. You were always able to shift-double-click an empty area next to a (text or graphical) link and shift-drag over the link to Quickblock it. And if you started the Quickblock attempt over a link, it would open in a new window (at least in Firebird) making it easy to try again starting the drag in an empty area.

I feel that with proper documentation the old behaviour would be really, really good.